This invention relates generally to an apparatus and to a process for cleaning a work piece, and more specifically, in one embodiment, relates to an apparatus and to a process for cleaning a plurality of work pieces and to efficiently maintaining the cleanliness of a scrubbing pad used in the process.
This invention relates to the processing of objects that are generally in the shape of flat, circular disks. Such objects include, for example, semiconductor wafers, compact disks, memory disks, optical blanks, and the like. Without loss of generality, such objects will be referred to as xe2x80x9cwork pieces.xe2x80x9d Illustrative examples will refer specifically to the use of this invention in connection with the processing of semiconductor wafers, but such examples are presented merely to aid in understanding, and are not intended to limit in any way the generality or application of the invention.
During the fabrication of a work piece, the work piece may be subjected to various processing steps. In the case of fabricating a semiconductor wafer, those process steps may involve the growth or deposition of insulating layers, the deposition of metal or other conductive layers, impurity doping, photolithographic patterning, planarization, and the like. The fabrication of such semiconductor wafers, like the fabrication of many other types of work pieces, requires extreme cleanliness of the wafer at various stages of the process. Accordingly, the above process steps are often preceded or followed by cleaning steps to insure that the requisite cleanliness is maintained.
Wafer cleaning, especially following a planarization step such as a chemical-mechanical planarization (CMP) process, often involves the scrubbing of the wafer surface with a cleaning pad, sponge, or brush. The scrubbing removes particulates, residue, and contaminates remaining on the wafer surface after the CMP process. A pad, generally in the form of a flat, circular pad, or a brush, generally in the form of a cylindrical roller, is often formed from a spongy material such as poly vinyl alcohol (PVA) or similar material. Although described above as xe2x80x9cflatxe2x80x9d or xe2x80x9ccylindrical,xe2x80x9d the pads or brushes may have bumps, ridges, or other projections on their surfaces to aid in the cleaning process. For ease of discussion, all such cleaning pads, sponges, and brushes will be referred to herein as xe2x80x9cpads,xe2x80x9d and the term shall be intended to include all such cleaning implements regardless of shape or material of construction.
For obvious reasons of economy, fabrication processes are usually designed for speed and efficiency. To achieve such speed and efficiency, it is desirable to process wafers serially, one after another, in an almost continuous and unending manner. The wafer cleaning steps should, preferably, lend themselves to such an efficient and continuous process. After the scrubbing of a wafer, especially following a CMP process, particulates are often found on or embedded in the surface of the pad. If not removed, these particulates can damage the surface of subsequent wafers when those subsequent wafers are scrubbed with the same pad. Semiconductor wafers are processed to fabricate device structures having extremely fine detail. Any scratching of such a device structure can cause the device to fail, resulting in a decrease in yield on the wafer and a decrease in the value of the wafer. Accordingly, it is clear that such damage to the surface of subsequent wafers is not acceptable. Present cleaning apparatus and processes have not been able to provide an efficient and speedy means to clean wafers without interrupting the almost continuous flow of wafers through the process.
A need therefore exists for a work piece cleaning process and apparatus that avoids damage to the surface of the work pieces being cleaned and that can be integrated into the overall work piece fabrication process. The work piece cleaning apparatus and process should preferably provide for cleaning of the cleaning pads on a regular basis without interrupting the cleaning of a plurality of work pieces.